Power presses are built in a wide variety of styles and sizes and those presses have a variety of applications, such as, forging, stamping, drawing, or other functions. A common construction of a power press is a double action press which combines the functions of blank holding with drawing. In many stamp and drawing operations, it has been found to be desirable to provide a die cushion which holds a blank to allow the metal of the blank to flow during working. A die cushion is often used to eject a worked blank. Die cushions come in various forms. A well known form is a rubber tankless type. Another well known form is a piston type which is an air cylinder assembly.
Die cushions utilizing an air cylinder assembly are generally a typical air cylinder construction having a cylinder and a piston movably relative to the cylinder. The construction of the air cylinder, as is conventional, utilizes various types of seals and packings to retain the air under pressure. The constant movement of the piston in the cylinder often results in wear in the seals and packing so that there is a constant loss of air from the cylinder, thereby causing the air to be wasted. The loss of air causes a needless operating cost in the operation of a press having an air cylinder die cushion. Importantly, the loss of air causes a variance in the holding force of the air cylinder resulting in a variance in the product produced by the press. In some instances, the variance causes some of the product to be unusable and thus be scrap.
The constant impact loading on a power press and die cushion causes wear to occur in the press and die cushion. It follows that it becomes necessary to maintain and repair the press as well as the die cushion. A desirable construction of a die cushion is one wherein the die cushion may be easily disassembled for maintenance or repair or the die cushion may be easily removed as a unit. Furthermore, it is desirable to provide a die cushion which has substantially no wear or air loss in operation.